Hugh Bowman played a pivotal role in tormenting Hartnell when aboard champion mare Winx, and now the gelding finally gets to benefit from the world's top rated jockey's expertise.
Bowman first gained a fresh perspective on Godolphin's 40-race veteran in a barrier trial earlier this month and races him for the first time in Saturday's Group One All Aged Stakes (1400m) at Randwick.
Hartnell last raced against Winx in last year's Group One Queen Elizabeth Stakes (2000m).
He has raced exclusively in Melbourne since James Cummings succeeded John O'Shea as Godolphin's head trainer in Australia, and he lines up in Sydney as Winx enjoys a spell before a crack at a fourth Cox Plate in the spring.
Bowman, who rode Winx to her 25th consecutive victory and 18th Group One in last Saturday's Queen Elizabeth Stakes at Randwick, admitted he was venturing into the unknown with one of Winx's regular adversaries.
He rode Hartnell for the first time at Warwick Farm on April 9 but said the 840m barrier trial hardly provided a useful insight.
"It was too short. I didn't get much of a feel of him," he said.
"I've got more of an understanding of him by watching him, than what I got by riding him."
Hartnell races in Sydney for the first time since the 2017 Queen Elizabeth Stakes, where he finished second, 5-1/4 lengths adrift of Winx.
Bowman said he always had admiration for Hartnell when riding Winx.
"I wouldn't say I was all that worried about him, but he's one I respected," he said.
"He's a class horse. This isn't his best trip but he's run very well over this trip before. I expect him to make his presence felt.
"Trapeze Artist is obviously the benchmark, he's an excellent young horse and the three-year-olds are doing well against the older horses with Alizee winning the Coolmore Legacy at the weekend."
Hartnell was a $9 chance with the TAB after the 13-strong field was finalised on Wednesday.
TJ Smith Stakes winner Trapeze Artist led the market at $2.20 while Brave Smash ($8) was the second elect.
Cummings was upbeat about Hartnell's potential to make a successful return to Sydney.
"He's back after a six-week break and looks nice and fresh coming into this race," he said.
Godolphin is also represented by seven-year-old gelding It's Somewhat ($26), who returns from a spell.
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